1. Field of the Invention
The present invention relates to devices and methods for determining position information, particularly for low power handheld devices.
2. Description of the Related Art
Locating the position of hand held devices such as cellular phones, personal digital assistants (PDAs) and wristwatches is becoming increasingly desirable for a number of reasons related to individual safety (e.g., locating the origin of 911 emergency calls), location based information services, personal navigation, etc. Position location based on the global positioning system (GPS) is becoming affordable because of the integration of most functions on a single chip. However, because of the great distance of the GPS satellites (over 20,000 km distant) the signal is extremely weak and requires great complexity, power and time to reliably detect, especially indoors or in cluttered urban environments with multipath signals. In addition, portable energy storage technology to support the higher power requirements of such systems, e.g. lithium batteries, is advancing very slowly. Hence, the practicality of continuous and/or autonomous position awareness remains poor.
System combining GPS and inertial sensors have been developed for navigational systems such as used on aircraft. However, the objective for such systems has been to improve or refine the accuracy of the GPS measurement. In general, these systems are large and expensive. In addition, the GPS operations for such systems operate continuously. Such systems have not been developed for small handheld devices to reduce power overall consumption.
There is a need for inexpensive devices and methods for determining position information of a user. There is also a need for such devices and methods for use in small handheld devices. Further, there is particularly a need for such devices and methods which operate at low power consumption levels. The present invention meets these needs.